BGL账号采用结构化的编号规则，即（）
A.9+机构号
B.货币码
C.业务标识
D.顺序号
参考答案：A, B, C, D
曳引式电梯机房平均噪声不大于（）DB.
A.55
B.60
C.70
D.80
We _____ last night, but we went to the concert instead. [ ]
A. must have studied
B. might study
C. should have studied
D. would study
